In general, a method of clamping and adhering metal sheets to each other by pressure is known as a method for joining metal sheets to each other. The joining by adhering by pressure depends on residual stress by clamping and contact, so that electric characteristics thereof are not satisfied. At a contact area of the metal sheets, there are many gaps so that it is has a problem that the electric characteristics cannot be easily maintained in a long period because of corrosion. For maintaining the electric characteristics, it is considerable to welding the metal sheets to each other by melting the metal sheets with gas or plasma. It is not easily to be automatized and not suitable for mass production and has a cost problem.
For overcoming the above problems, a patent document 1 proposes a method for joining sheet metals, in which the metal sheets 110, 111 are joined as shown in FIGS. 10, 11 by cutting the two metal sheets 110, 111 along a cutting line L2 from one end of a bending line L1, extending vertically apart from the bending line L1, toward the other end of the bending line L1, and by pressing and bending an area surrounded with the cutting line L1 and bending line L2 of the two metal sheets 110, 111 about the bending line L1. According to the method, outer surrounding cutting surfaces along the cutting line L2 of the metal sheet 110 is pushed so as to rub on inner surrounding cutting surfaces along the cutting line 2 of the metal sheet 111. By rubbing on each other, oxidized surface thereof is removed and fresh surface is exposed, and the both outer and inner cutting surfaces are adhered so as to generate a metal contact area of the metal sheets. A metal joint body 101 having the metal contact area is provided with a pair of projecting members 113 projecting in a pressing direction (i.e. arrow Z) by pressing the area surrounded with the cutting line L2 and the bending line L1. Each one of the projecting members 113 is formed into a trapezoidal shape in a top view, and arranged with a space therebetween so as to oppose each short side (i.e. the bending line L1) of the pair of projecting members 113 formed into the trapezoidal shape.
A die used for pressing the two metal sheets 110, 111 includes a pair of press jigs formed gradually narrowing toward a top end thereof. The pair of press jigs is arranged with a space corresponding to the pair of projecting members 113 formed into a trapezoidal shape.